The thing is, if we want to do something like that, the energy cost to launch the equipment to break down rocks (or water ice, even) for hydrogen would be much greater than the cost of launching a tank of hydrogen. I mean, you'd have to have some sort of mobile scoop, crushers (which would need lots of power), heaters, cleaner/refiners, etc.

and my guess is that the first real ISRU device we send will be simple. unless it's NASA.

From these, I see that the required delta-v from Mars surface to LEO is 6.6 - 7.8 km/s, while the delta-v from Earth surface to LEO is 9.7 km/s, due to gravity difference, I guess. so in deltaV, it's cheaper to ship from Mars to LEO than it is from Earth to LEO.

This made me wonder. An ISRU methane fuel generation plant on Mars that sends fuel to LEO may be more economical than simply launching fuel from Earth. In conjunction with on-orbit refueling, this could possibly lower the cost of, for instance, a manned Mars Mission, which requires the huge EDS with all its fuel.

I'm sure I'm discounting lots of complexity and details, though, so it may not actually be cheaper.

To produce methane on Mars, you still need hydrogen from Earth. My books are currently not available as I move house but I have in mind something of a faction like 1 ton hydrogen:3 ton methane (+ oxygen).
I can check the values the next days.

_________________"The hardest hurdle to space isn't the technicalities and money. But rather, the courage and the will to do it." - Burt Rutan.

there is a lot of hydrogen on Mars. It is not only that bound in water but in acids too that Spirit and Opportunity have found.

This moment I am wondering if you might be thinking of oxygen but this also is available on Mars - and also bound in acids but not only in water.

There are teams working on technologies to get oxygen out of lunar Regolith - they are competing for a Centennial Challenges Prize. On of those teams is working on a technology that cracks down each molecule into the elements it is made of. This is done using solar light and a parabolic mirror. This technology could be applied on Mars also - it simply would have to be larger.

This technology or any technology doing or acchieving the same removes the requirement to carry hydrogen or oxygen from Earth to Mars as far as I understand it.

What is the reason why hydrogen or oxygen would have to be carried from Earth to Mars?

Hello, JesseD, I think it to be likely that you are right. You already listed the reason - the different gravity. The escape velocity at Mars is less than at Earth - in particular if the vehicle is in orbit already.

When the vehicle has left the martian orbit no more fuel needs to be consumed except for course corrections. And since there is an infinite number of orbits around Earth very lot of which or on different altitudes it seems to be possible to enter an earthian orbit at the same velocity as the martian orbit was left. This orbit simply would be on a higher altitude above Earth than the martian was above Mars.

If each interplanetary mission would have to depart from that orbit there is no problem with your result I think. Even the way down to Earth could then be made using the cheap delivereies from Mars.

This all can be checked to some degree when the Excel spreadsheet I am working on in the Lunar Soyuz-thread in the Financial Barriers section is ready to be extended to the ability to calculate interplanetary missions by reusable vehicles.

The requirement for bringing hydrogen from Earth comes from the Mars Society plan called "Mars Direct". It was created at a time when there was doubt about the amount of water on Mars. Here is a quote from the web site at http://chapters.marssociety.org/toronto ... rect.shtml .

Quote:

The Martian atmosphere consists almost entirely of carbon dioxide, which can be transformed via chemical reactions, along with a small quantity of hydrogen brought from Earth, into rocket fuel. This results in up to 18 kilograms of rocket propellant being produced for every kilogram of hydrogen supplied

Given that we now are pretty sure there is lots of water on Mars, this plan is kind of out of date. It does have the advantage of simplicity though. A tank of hydrogen is simpler than a drill and maybe a tractor or other equipment with moving parts that could break down. A pump to compress CO2 directly out of the air is a pretty simple machine and some kind of pump would be needed with water anyway. Obviously that would not be such a good option for a long term base or settlement because of the need for repeated hydrogen deliveries, but for a sortie mission it is pretty good.

What is the reason why hydrogen or oxygen would have to be carried from Earth to Mars?

Note: this assumes LOX/Methane rocketry.
As Campbelp2002 noted, a small amount of Hydrogen can be leveraged relatively easily into CH4 and LOX:

4H2 + CO2 --> CH4 + 2H2O --> CH4 + 2H2 + 2O2

The system, as tested on Earth by Zubrin et al, required some energy input, (<30W for initial core heater, <130W for electrolysis of H2O ) but was self-contained. The reaction is exothermic once started, and ran at <1 atm pressure.

A system to utilize local water would require the system to move to the local water ice, dig or melt it, and electrolyze it, whereas a system using imported hydrogen could land with almost empty tanks (on a LOX/Methane rocket), spread out some solar panels, open an input port, and start sucking in CO2 and refilling its LOX and methane tanks. a week or two later, it closes up shop, and blasts off for LEO with a full load. In LEO, it could unload its fuel, leaving only enough to get back to Mars, and trade it for another payload of LH2.

A rocket which launched directly from Earth to Mars, landing almost empty, could refill, launch back to LEO, offload 1.9 km/s worth of fuel, and still get back to Mars for another load.

I recall that an early version of SpaceX's Falcon 5 was designed to launch with a half-empty stage. If this idea were to be utilized, the system could be even more efficient. I.e., a rocket that could hold 20km/s dV of fuel, but only launched with fuel for 13.4 km/s, could bring back 8.5 km/s worth of fuel to LEO.

This would most likely require a SSTO system, right?
Or something like Armadillo Aerospace's system...
just some mental bubblings.

what you say menas that the requirment to carry hydrogen from Earth is a consequence of the choice of equipemtn, technology or/and concept merely than a requirment caused by nature or availability of ressources.

In difference to that I am looking at it NOT from the equipemtn, technology or concept but from the nature and the availabilities - and then according to these the equipmen and technology are chosen and the concept designed.

AAt present several probes are still lokking where there is water ice on Mars. One location seems to be a sea at the equator or at least closer to it than to the poles and the thick layers of ice at the poles.

The talk is about water here - but it is also supposed that H2O2 may be to be found at several locations because dust devils are suspected to cretae it.

Next there are several reasons to land where water is in larger amounts:

increased probability to find nacient or present microbial lifemanned missions require access to waterreserach for the probable ingredients of former martian water cvering the planet

In so far there is a probability that future missions will land where the water is nonetheless In that case the half-empty-tank-argument is speaking for concepts that don't carry hydrogen from Earth merely. What SpaceX has ssiad had to do with payloads merely that are much lighter than the capacity of the F alcon 5.

Regarding Mars a lighter tank because of refuelling by ISRU sill be much more interesting. This can be explored better when the excel spreadsheet I am working on is enabled to calculate martian trips.

A single vehicle roundtrip from Mars surface to Earth LEO, dropping fuel and returning would be almost impossible. The mass ratio would be forbidding.

A much better idea is to build a depot in Mars orbit or on Phobos.
Launch CH4 & LOX to there fron the surface with a dedicated lander/tanker. Use a separate transfer/tanker to move it from there to LEO or L2. If there's any water on Phobos you caould make LOX & LH2 there as well.

what you say menas that the requirment to carry hydrogen from Earth is a consequence of the choice of equipemtn, technology or/and concept merely than a requirment caused by nature or availability of ressources.

In difference to that I am looking at it NOT from the equipemtn, technology or concept but from the nature and the availabilities - and then according to these the equipmen and technology are chosen and the concept designed....

However, I had been trying to think about how such a system would work.
If such a system were designed and actually built, its goal or purpose would be to bring as much fuel to LEO as possible, autonomously.
Any system's chances of working flawlessly generally decreases as the complexity of that system increases. This would be especially true for mechanical systems with moving parts, like pumps, crushers, conveyers, etc. You want a system that you can launch and forget about -- or at least not have to launch a rescue mission.

I agree that the resources to utilize in situ hydrogen are there, but the mechanical complexity, weight, and 'wear and tear' would most likely decrease the usefulness of the system.

- Jesse

Oh, and as for the numbers. Like I said, I was just doing quick 'back-of-the-napkin' calculations.. I'm sure there are more variables I didn't consider.

There are some aspects that mean that the complexity problem is removed:

LOX/Metahne engines already are under development and construction
QuickReach consumes LOX/Propane - propane could be produced on Mars as well as Methane
reusable vehicles are under develoment

This short list means that a vehicle going to Mars may be a resuable one that might consume LOX7Methane. In that case system-complexity already is managed and working well. Propane-production on Mars is looking to be waste but what if working reusable LOX/Propane-engines are available earlier than reusable LOX/Methane engines?

Because of this the system complexity of the vehicles will be solved.

This means that also fuelling and refuelling is solved - regardless of the fuel being Metahne, Propane, LH2 or something else.

Then the production of the fuel can be kept out of the vehicle. This production also is solved already.

This is a simply way already available. It could be improved for and adjusted to Mars.

I am starting to suppose that the complexity you are talking about is the complexity of a vehicle into which the production of fuel is integrated - is that right? If yes I agree - but this would be one single mission at which considerations of deliveries mustn't or shouldn't be based on.

With regard to delivery of water ice for processing into lox/methane why not put the production rig on wheels and move to where the deposits are?

It could park itself over a suitable site and suck up the ice. It could either fill up on board storage tanks wwith LOX and methane which it could periodically discharge into fixed storage tanks or just melt the ice and store as water that can be pumped to a processing plant.

This has the advantage of working a larger area and being able to choose the richest deposits.

_________________A journey of a thousand miles begins with a single step.

Any dependence on using material from the surface would create the need to be mobile, or have a separate rover to go to there the desired deposits are. But it may be 500km to the nearest water! We have some idea of where the water is, but we are not completely sure it is accurate information. Unless we know for sure there is water within a few meters, or maybe a couple kilometers, of the landing site then a system that only uses the atmosphere has a big advantage; possibly big enough to outweigh the disadvantage of bringing extra consumables from Earth.

There are some aspects that mean that the complexity problem is removed:

LOX/Metahne engines already are under development and constructionQuickReach consumes LOX/Propane - propane could be produced on Mars as well as Methanereusable vehicles are under develoment

yes, this is true, and I had been assuming the system useds methane/LOX

Ekkehard Augustin wrote:

This short list means that a vehicle going to Mars may be a resuable one that might consume LOX&Methane. In that case system-complexity already is managed and working well. Propane-production on Mars is looking to be waste but what if working reusable LOX/Propane-engines are available earlier than reusable LOX/Methane engines?

That was also what I had assumed: that the vehicle going to mars was a highly reliable, reusable, 'space tug'. Such a system would not need to be terribly complex: fuel and oxidizer tanks, a regeneratively-cooled engine, a reliable computer control system

Ekkehard Augustin wrote:

Because of this the system complexity of the vehicles will be solved.This means that also fuelling and refuelling is solved - regardless of the fuel being Metahne, Propane, LH2 or something else.

This is what I had NOT assumed.

Ekkehard Augustin wrote:

Then the production of the fuel can be kept out of the vehicle. This production also is solved already. This is a simply way already available. It could be improved for and adjusted to Mars.

I am starting to suppose that the complexity you are talking about is the complexity of a vehicle into which the production of fuel is integrated - is that right? If yes I agree - but this would be one single mission at which considerations of deliveries mustn't or shouldn't be based on.

I was thinking of a system specifically designed solely to acquire and deliver as much rocket fuel as possible to LEO.

The most efficient system I can think of would be a single vehicle which is has as low a complexity level as possible. To me, having a separate vehicle for the production of fuel using in situ water ice adds several levels of complexity. One, you would need separate power and control systems. Two, you would need a system that is mobile, like the current Mars Rovers. (the rovers have had several problems, like broken wheels, power losses, getting stuck in the sand, etc.) Three, you need a system which can acquire and melt water ice. this means multiple levels of interaction with the Martian environment (grinders, melters, filters, etc), which introduce more possibilities for system failure and 'tear and tear' which could not be easily rectified. i.e., NASA can't fix the broken wheel on the one Mars Rover, the little guy has been limping backwards across the plains of Barsoom for months now, dragging its broken wheel behind it. Four, you need a system that can transport itself back to the 'tug' and refill it; or a tug that can land within reach of the fuel generator.

Andy Hill wrote:

With regard to delivery of water ice for processing into lox/methane why not put the production rig on wheels and move to where the deposits are?

It could park itself over a suitable site and suck up the ice. It could either fill up on board storage tanks with LOX and methane which it could periodically discharge into fixed storage tanks or just melt the ice and store as water that can be pumped to a processing plant.

This has the advantage of working a larger area and being able to choose the richest deposits.

The other problem with this, as Campbelp2002 notes, is that most of the water ice is at the martian poles. A system which shuttles back and forth between Mars and Earth should be as energy efficient as possible. It takes a lot more energy to land at the poles of a planet than it does to land near the equator, because you have to burn lots of fuel making plane changes.

It seems to me that the simplest system, specifically designed solely to acquire and deliver as much rocket fuel as possible to LEO, should be able to take the lowest-energy paths between those two destinations, which would preclude polar landings. it should be self-contained, having as little interaction with the Martian environment, thereby minimizing the wear and tear on the system. it should be a system that, if the environmental hazards DO cause the fuel generation system to break (i.e., a dust devil jumps into the CO2 intake pump and clogs it up ), can be returned to Earth and repaired. A single vehicle with an integrated fuel generation system could concievabley fly itself back to LEO for repairs.

My mother always told me, "don't let something good keep you from reaching the best." In this case, I think it should be, "don't let striving for the best keep you from ever reaching the good."
I agree, a purely in situ, self-sufficient system that needs nothing from Earth would be great, but the complexity and potential problems might prevent any system at all from ever lifting off.